Eccentric Core Fiber Research Articles

Two-Axis Bending Sensor Based on Cascaded Eccentric Core Fiber Bragg Gratings

A two-axis bending sensor based on cascaded eccentric core fiber Bragg gratings (ECFBGs) is presented and demonstrated. The sensor is fabricated by independently writing two FBGs in two ECFs, which are spliced with orthogonal core-offset directions. Each ECFBG is most sensitive at the core-offset direction and insensitive at the perpendicular direction. When one ECFBG is in the state of most insensitive to bend, the other ECFBG must be in the most sensitive state. Therefore, the cascaded ECFBG structure can easily realize 2-D bending measurement. The sensor's spectral responses to the curvature at different bending directions are experimentally investigated. The maximum curvature sensitivities of the two ECFBGs are 37 and 39 pm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively, within the curvature range from 0 to 8.18 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> .

Pure Directional Bending Measurement With a Fiber Bragg Grating at the Connection Joint of Eccentric-Core and Single-Mode Fibers

A novel fiber Bragg grating (FBG) structure based on an eccentric core fiber (ECF) and a single-mode fiber (SMF) was proposed and experimentally demonstrated for distinguishing the bending effect from the axial strain effect and measuring the pure directional bending. The structure is fabricated by writing a FBG on the fusion splice junction between an ECF and a SMF. The FBG formed on the ECF-SMF junction has two different resonant peaks because of the different refractive indices of the two fibers. The peak relating to the ECF is sensitive to both directional bending and axial strain, while the peak corresponding to the SMF is only sensitive to strain. By using the unique FBG structure, one can directly know whether a bending is accompanied by an axial strain, and can obtain both the direction and curvature of the bending. Experimental results show that the bending sensitivities of the FBG in the ECF part are 49.3 and −50.3 ${\rm{pm}}/{{\rm{m}}^{ - 1}}$ at directions of 0° and 180°, respectively, and the strain sensitivities of the FBG in the ECF and SMF are 0.74 and 0.70 pm/μϵ, respectively.

Distributed fiber surface plasmon resonance sensor based on the incident angle adjusting method.

We propose and demonstrate a distributed surface plasmon resonance (SPR) fiber sensor based on a novel, simple, and effective incident angle adjusting method. For normal fiber SPR sensors, it is hard to realize distributed sensing because it is hard to produce two dynamic ranges (resonance wavebands) with a great difference. The dynamic range depends on the incident angle, and therefore, we propose an incident angle adjusting method that is implemented by grinding an eccentric-core fiber to different angles, which helps to produce different SPR wavebands with great difference, thus realizing distributed sensing. In our two cascaded distributed configuration, with the refractive index range of 1.333-1.385, the fiber grind angles are 9° and 17°, the testing wavelength ranges are 613-760 nm and 745-944 nm, and the average testing sensitivities are 2826 nm/RIU and 4738 nm/RIU, respectively. Larger resonance wavelengths are associated with larger testing sensitivities. This distributed fiber sensor has important significance in the fields of multichannel liquid refractive indices and temperature self-reference measurements.

Fiber-Optic Ammonia Sensors Utilizing Rectangular-Cladding Eccentric-Core Fiber

A new fiber-optic ammonia sensor utilizing rectangular-cladding eccentric-core fiber and a sensitive film containing an indicator dye is demonstrated. The sensitive film is a SiO2-GeO2 gel film including an indicator dye of bromocresol purple or bromocresol green, which is dip-coated by a sol-gel technique. The attenuation of this sensor changes depending on the concentration of ammonia at the wavelength range of 500–700 nm. This sensor can detect several ppm of gaseous ammonia. Various factors determining the sensitivity to detect the ammonia gas and time response of the sensor are also studied.

Computations of optical birefringence characteristics of highly eccentric elliptical core fibers under various thermal stress conditions

The birefringence characteristics of optical fibers with a highly eccentric elliptical core are investigated under various thermal stress conditions. A new numerical method for solving the vectorial Maxwell equations is proposed which simultaneously takes into account the effects of ambient temperature and the geometrical distribution of the refractive indices of anisotropic propagation media. To verify the reliability of our numerical procedure, the birefringence characteristics are investigated of a highly birefringent elliptical core fiber used recently in the design of an optical sensor. The birefringence characteristics calculated by this procedure and those obtained from models currently used in the field of fiber-optic sensing devices are compared with experimental data. For highly birefringent fibers, the numerical method proposed is far more accurate.

Propagation characteristics of eccentric core fibers using point-matching method

The propagation characteristics of homogeneous single-mode optical fibers with eccentric core are analyzed by a numerical method based on the Improved Point-Matching Method (IPMM). The variation of fundamental mode propagation constant has been computed for various eccentricities with different fiber parameters.